1. Field of the Invention
The present invention relates to an improvement of a control system for a fan coil which is used for air-conditioning the inside of a room by means of a fan for heat exchanging and a coil in which cool or hot water is circulated.
2. Description of the Related Art
In a known control system for a fan coil of an air-conditioner, the cooling or heating operation is automatically activated in response to whether the monitored water temperature rises or falls to a predetermined threshold temperature. For example, when cool or hot water is below 25.degree. C., the control system automatically changes to the cooling operation, and when cool or hot water is above 25.degree. C., the control system automatically changes to the heating operation. The control system thereafter operates its air-conditioning in response to the difference between a target room temperature and a monitored room temperature for a set operation time. For energy saving, the target room temperature is occasionally set, for example, to 23.degree. C. at its highest limit in the heating operation, or to 25.degree. C. as its lowest limit in the cooling operation. At such a setting, however, neither the cooling operation nor heating operation is activated, with a room unit for which is also left inoperative, when the room temperature is, for example, 24.degree. C., typically in mild temperature seasons. Even in this case, blowing is still needed to keep room at a comfortable temperature. Air-conditioners normally have LEDs (Light Emitting Diode) to indicate their status of heating or cooling operation. Under the above temperature setting, when the water temperature is, for example, at 25.degree. C. or lower, air-conditioners, regardless of their inoperative status, indicate with LEDs that the cooling operation is now under way. This may mislead the user.
In view of the above-mentioned disadvantage, an improved control system for a fan coil has been proposed (see Japanese Laid-Open Utility Model Publication No. 2-48738). In such a system, an automatic switching between the heating and the cooling operation is allowed by monitoring water temperature, and a blowing operation is provided between the cooling and heating operation in order to save energy and maintain a good air temperature, and further, wherein a message on the operational status of the control system is correctly indicated so that the user is not mislead by the indication.
While, an air-conditioner as above-mentioned which performs cooling or heating by using cool or hot water, a monitored temperature of the cool or hot water serves as a reference for automatic switching from the cooling operation to heating operation, or vice versa, and the room temperature is controlled by an electromagnetic valve which opens or closes for the cool/hot water to circulate or not to circulate. Such air-conditioners suffer from the problems discussed below. During the winter, for example, a controller is set to OFF, causing an indoor fan coil unit to be inoperative, the electromagnetic valve closes blocking the flow of hot water. Hot water then gets cold enough for a water temperature sensor to signal the air-conditioner to be in the cooling operation. If the controller is now set to ON, the electromagnetic valve remains closed during automatic operation because the room temperature is low. The heating operation remains inoperative indefinitely.